So… I have an embarassing confidence to make.
A friend and I spend our evening and found a way to fix the problem… using Debian Testing.
I have a dual boot Nixos / Ubuntu. And the sound problem was on both OS. So we decided to wipe the Ubuntu and install Debian Testing. Doing this restablished the sound on Debian.
I remarked that now, doing a lsmod now displays more output, and especially related to driver snd_hda*:
❮onyr ★ nixos❯ ❮~❯❯ lsmod | grep snd
snd_seq_dummy 12288 0
snd_hrtimer 12288 1
snd_seq 110592 7 snd_seq_dummy
snd_seq_device 16384 1 snd_seq
snd_sof_pci_intel_tgl 12288 0
snd_sof_intel_hda_common 245760 1 snd_sof_pci_intel_tgl
snd_soc_hdac_hda 28672 1 snd_sof_intel_hda_common
soundwire_intel 81920 1 snd_sof_intel_hda_common
snd_sof_intel_hda_mlink 36864 2 soundwire_intel,snd_sof_intel_hda_common
snd_sof_intel_hda 20480 1 snd_sof_intel_hda_common
snd_sof_pci 24576 2 snd_sof_intel_hda_common,snd_sof_pci_intel_tgl
snd_sof_xtensa_dsp 16384 1 snd_sof_intel_hda_common
snd_hda_codec_realtek 200704 1
snd_sof 425984 3 snd_sof_pci,snd_sof_intel_hda_common,snd_sof_intel_hda
snd_hda_codec_generic 110592 1 snd_hda_codec_realtek
snd_sof_utils 16384 1 snd_sof
snd_hda_ext_core 36864 4 snd_sof_intel_hda_common,snd_soc_hdac_hda,snd_sof_intel_hda_mlink,snd_sof_intel_hda
snd_soc_acpi_intel_match 94208 2 snd_sof_intel_hda_common,snd_sof_pci_intel_tgl
snd_soc_acpi 16384 2 snd_soc_acpi_intel_match,snd_sof_intel_hda_common
snd_soc_core 450560 4 soundwire_intel,snd_sof,snd_sof_intel_hda_common,snd_soc_hdac_hda
snd_hda_codec_hdmi 98304 2
snd_compress 28672 1 snd_soc_core
ac97_bus 12288 1 snd_soc_core
snd_pcm_dmaengine 16384 1 snd_soc_core
snd_hda_intel 65536 2
snd_intel_dspcfg 36864 3 snd_hda_intel,snd_sof,snd_sof_intel_hda_common
snd_intel_sdw_acpi 16384 2 snd_sof_intel_hda_common,snd_intel_dspcfg
snd_hda_codec 217088 6 snd_hda_codec_generic,snd_hda_codec_hdmi,snd_hda_intel,snd_hda_codec_realtek,snd_soc_hdac_hda,snd_sof_intel_hda
snd_hda_core 139264 9 snd_hda_codec_generic,snd_hda_codec_hdmi,snd_hda_intel,snd_hda_ext_core,snd_hda_codec,snd_hda_codec_realtek,snd_sof_intel_hda_common,snd_soc_hdac_hda,snd_sof_intel_hda
snd_hwdep 20480 1 snd_hda_codec
snd_pcm 184320 11 snd_hda_codec_hdmi,snd_hda_intel,snd_hda_codec,soundwire_intel,snd_sof,snd_sof_intel_hda_common,snd_compress,snd_soc_core,snd_sof_utils,snd_hda_core,snd_pcm_dmaengine
ledtrig_audio 12288 2 snd_hda_codec_generic,asus_wmi
snd_timer 49152 3 snd_seq,snd_hrtimer,snd_pcm
snd 151552 19 snd_hda_codec_generic,snd_seq,snd_seq_device,snd_hda_codec_hdmi,snd_hwdep,snd_hda_intel,snd_hda_codec,snd_hda_codec_realtek,snd_sof,snd_timer,snd_compress,snd_soc_core,snd_pcm
soundcore 16384 1 snd
led_class 20480 6 snd_hda_codec_generic,videodev,input_leds,iwlmvm,asus_wmi,nouveau
Rebooting on NixOs, the problem was gone. So it must be a black-magic microcode / firmware / kernel module hell.